Adoptive immunotherapy with large numbers of in vitro expanded antigen-specific CDS T cells has the potential to become a novel and safe treatment modality for cancer or viral infections, but efficacy is often limited. One obstacle is insufficient in vivo survival and retention of function by donor T cells, which can often be sustained by cotransfer of CD4 helper T cells or by IL-2 administration to substitute for CD4 help. However, specific helper CD4 T cells have not been identified for many tumors, CD4 T cells are often limiting and can be pose additional problems during treatment of HIV infection, and prolonged high-dose IL-2 supplementation can be both inefficient and toxic. Another major obstacle to adoptive immunotherapy can be the failure of transferred T cells to be effectively activated by viral and tumor targets in vivo. T cells specific for tumors often have low affinity TCRs, malignant or infected targets can have impaired antigen processing machinery or accessory signals, and prolonged recognition of target cells can induce T cell tolerance. Thus, increasing the capacity of CDS T cells for IL-2 production and autocrine IL-2 mediated proliferation, reducing the threshold for CDS T cell activation, or preventing induction of tolerance in antigen-specific CDS T cells should significantly enhance the efficacy of adoptive immunotherapeutic strategies. One potential means to increase CDS T cell avidity and function or sustain autocrine IL-2 proliferation and survival is to reduce inhibitory signals in transferred CDS T cells mediated by intracellular regulatory proteins. We have identified Cbl-b, SHP-1, and SOCS-1 as potential targets to enhance CDS T cell aviditiy and function. CDS T cells from mice deficient in these genes results in increased T cell reactivity and costimulation independent IL-2 production. The major goals of this project are to determine if decreasing the negative regulation of activation signals in CDS T cells by Cbl-b, SHP-1, or SOCS-1 by expression of dominant negative versions of these proteins, or by reducing endogenous levels of these proteins via expression of specific siRNA, can improve T cell avidity and function and render these cells more effective in therapy of chronic viral infections or malignancy in mouse models. Additionally, we will determine if abrogating inhibition by these regulatory proteins can enhance the avidity, proliferation and survival of human CDS T cells in preclinical studies. Chronic viral infections and cancer represent major public health concerns. Adoptive immunotherapy with T cells has the potential to become an effective and broadly applicable approach for the treatment of viral infections and malignancy. However, the efficacy of transferred T cells is limited by insufficient in vivo survival and function. These studies will determine if genetically modifying T cells to improve function and survival can enhance adoptive immunotherapy approaches in mouse models of chronic viral infection or malignancy as well as the survival and function of human virus and tumor specific T cells in preclinical studies.